Flat sheets of corrugated paperboard have been used many years as the starting material in forming containers. Corrugated paperboard generally refers to a multilayer sheet material comprised of two sheets of liner bonded to a middle corrugated layer of medium. Usually, the corrugated container plant of today is located relatively close to its customer base and includes a corrugating and laminating machine to form the paperboard and thereafter, usually in-line, slitter-slotter-scoring machines and printing and packaging machines. The liner and medium paper rolls will normally come from paper mills which generally tend to be located close to their source for raw materials.
One style of container is the single-piece tray type where a single piece of corrugated paperboard will be cut and scored to form a flat blank which will then be erected into a container with four sides and a bottom. Oftentimes, closure flaps will be designed into the single-piece style. Some of these designs are provided with features to allow hand setup at a using facility while others are designed for machine setup where cooperating adjoining portions are adhesively bonded to form the container. Quite commonly, these types of containers are used for holding fresh fruits and produce from packing and shipping to display at the retail level.
Usually when packing a particular product such as tomatoes, peaches, mangos and the like there is a typical size requirement in that the container volume is sized to hold a certain amount of product. There is also a strength requirement given the weight of product packed and the stacking, shipping and handling requirements. Of course, the paperboard material provides certain of the structural strength depending on the grade of paper used in its formation. Heavier paper grades provide greater strength in stacking and bursting. The structure of the container can add greatly to its strength properties.
Typically a packed container of produce will hold a weight suitable for handling by an individual. Such containers will be generally rectangular and have a variable height dimension ranging from three to twelve inches. Further, these containers will normally be stacked for transport and storage.
Given the basic size requirement specified by the customer it is then an effort to provide the structural stacking strength with the optimum amount of corrugated paperboard. A typical well known single piece container design is one having a bottom, two side walls hinged to the bottom and at least two end walls hinged to the bottom. To form the container the walls are folded upwardly to be normal to the bottom and then connected to form the containment volume within the four walls. Variations are well known where top closure flaps are hinged to the top edges of the side walls and for stacking strength a second end wall can be hinged to the top edge of first end wall to then form a double layer of paperboard thereby enhancing the stacking strength. Additional known features used in such containers include, for example, additional panels hinged to the end wall side edges which are used to form vertical inclined corner posts and additional layers along the side walls to likewise enhance stacking strength. When even greater stacking strength is required, additional foldable panels can be added to yield three or four ply end wall variations. When providing such containers, it is an objective to provide the maximum stacking strength utilizing the least amount of material while at the same time providing all of the other features specified by the customer, such as stacking tabs, hand holds, vent holes and the like.
One objective of the present invention is to provide a single piece container blank which utilizes reduced material with the same or enhanced stacking strength.
Another objective is to provide a container with multiply end walls utilizing less material which has the same or enhanced strength.
Yet another objective is to provide a trapped stack tab as a part of the multiply end wall construction with sufficient structure to resist "fold over" during use.
These and other objects of the invention will become apparent upon reading the specification to follow in combination with the attached drawings.